Aluminum conductors



United States Patent 3,383,188 ALUMINUM CONDUCTORS Christian E. Michelson, Hamden, Conn., Charles M. Fredrickson, "Chattanooga, Tenn., and James F. Murphy, Hamden, Conn., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Sept. 27, 1965, Ser. No. 490,660 Claims. (Cl. 29--183.5)

The present case relates to aluminum base alloy conductors. More specifically, the present invention resides in aluminum base alloy conductors having improved current carrying capacity.

Aluminum alloy conductors are widely used commercially and therefore improvements in this area are highly desirable.

The size of electrical transmission conductors is determined by a variety of factors. In the case of some lines, the size is determined by the ability of conductor to lose the heat generated as a result of current flow. The heat must be lost rap-idly enough to prevent the temperature from exceeding 100 0., otherwise the strength of the conductor will be adversely effected.

The current carrying capacity of the line is limited by the temperature rise of a conductor which in turn is caused by the ohmic losses associated with the current flow. As stated above, generally the conductor temperature is not allowed to exceed 100 C. The heat generated in the conduct-or can be lost only through radiation and convective transfer of energy. Convective losses are determined by the air temperature, pressure and movement which are largely uncontrollable variables. On the other hand, that portion of the heat generated in the conductor which is lost by radiation is determined by the emittance of the surface,

For example, a bare, shiny unweathered conductor has a low emissivity and, therefore, a lower permissible current carrying capacity for the same allowable temperature rise.

Emittance may be measured in a vacuum apparatus by determining the rate of radiation from a heated surface to the walls of the chamber. The value for emittance is the ratio between the rate at which a particular body radiates heat to that at which a black body at the same temperature radiates heat. The higher the emittance the more heat is lost per unit of time by radiation. When associated with electrical transmission conductors, the higher the emittance and the greater the amount of heat which is lost, the greater the current carrying capacity.

For example, pure aluminum generally has an emittance of less than 0.10 and stranded aluminum transmis. sion cable seldom shows an emittance greater than 0.25.

Prolonged exposure to the elements results in the buildup of natural corrosion products, soils and other absorbing layers which increase the emittance of the surface. This process occurs in an unpredictable way since it is dependent upon variable exposure environments. Because the variation is so unpredictable, little or no actual advantage is obtained due to the increased emittance. In any event, the increased emittance attained by these natural causes is generally not predictable enough to result in usea ble improved current carrying capacity.

It is, therefore, an object of the present invention to provide an improved conductor.

It is a further object of the present invention to provide an aluminum base alloy conductor of improved current carrying capacity, with the attendant advantages attained therefrom, while retaining the other desirable physical properties of the conductor.

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provide a conductor as aforesaid having a pleasing physical appearance and good corrosion resistance.

It is an additional object of the present invention to provide a conductor as aforesaid which is prepared by simple and inexpensive treatments.

A still further object of the present invention is to provide an improved aluminum base alloy conductor having increased emittance which thereby allows more rapid dissipation of heat generated as a result of current flow.

Further objects and advantages of the present invention will appear hereinafter.

In accordance with the present invention it has now been found that the foregoing advantages may be readily attained.

The present invention resides in an aluminum base al- 'loy conductor of improved current carrying capacity having a diameter of at least 0.050 inch and having an IACS conductivity of at least 50, said conductor having a surface oxide coating of at least 0.01 mil in thickness with the surface of said conductor having an emittance ratio of from 0.35 to 1.0.

In accordance with the present invention it has been surprisingly found that the foregoing conductor effectively attains all of the objectives of the present invention and results in a greatly improved conductor with current carrying capacity being increased generally on the order of about 10%. Further, it has been found that the increased current carrying conductor of the present invention has corrosion resistance and physical properties comparable to the untreated conductor. In addition to this the improved conductor of the present invention is characterized by having a less shiny, slighttly colored appearance which is a desirable quality especially where the conductor is placed in highly developed suburban residential areas.

A further advantage of the present invention is that the improved conductor has a smoother surface as a result of the treatments of the present invention and therefore is less likely to radiate energy because fewer sharp projections exist,

A particular advantage of the present invention is that the improved conductor is readily and conveniently obtained. In addition, the increased emittance of the surface results in more rapid dissipation of the heat generated as a result of current flow.

The improved conductor of the present invention may be any aluminum base alloy. By aluminum base alloy is meant any al-loy having a major portion of aluminum. For example, high purity aluminum, EC aluminum, aluminum alloys 5005, 6062, 6201, 1100, etc.

The conductors of the present invention should have an IACS conductivity of at least 50 and a diameter of at least 0.05 inch.

The conductors of the present invention may be used in single strands or with three or more aluminum base alloy conductors stranded together to form a stranded cable. The stranded cable may be utilized either with or without steel reinforcing.

The shape and diameter of the strands in the conductors of the present invention is not critical and any desired shape or convenient diameter may be used.

The conductor of the present invention has a surface oxide coating of at least 0.01 mil thickness. The preferred thickness range is from 0.05 to 0.3 mil. Thicker coatings may be utilized but these offer small additional improvements and are not economical to obtain. In addition, the surface conductor has an emittance ratio between 0.35 and 1.0 and preferably 0.4 and 0.8. Emittance has been defined above and the manner in which it is measured has also been defined. The greater the emittance the more 3 heat is lost per unit of time by radiation and thus the greater the current carrying capacity of the line.

The conductor of the present invention may be prepared by any of the known methods. The preferred treatment is an electrolytic treatment to convert a portion of the metal at the surface of the conductor into an oxide. Anodizing is an example of this process whereby an oxide is formed which contains not only the aluminum and oxygen by significant quantities of water and the anion of the forming electrolyte as well. Anodizing is the preferred process by which increased radiation from the conductor is obtained.

Preferred anodizing electrolytes are dilute aqueous sulfuric and dilute aqueous oxalic acid solutions although a variety of others may be conveniently employed. Such as, for example, chromic acid and phosphoric acid. The anodizing may of course be done over a wide range of current densities. The preferred being the highest obtainable within the limits of supply and attainable agitation and cooling. Practical limits of available equipment generally limits this to about 1000 amps per square foot. The concentration of the electrolyte in the bath is also not patricularly critical. The preferred material concentration is for oxalic acid between 5 and aqueous solutions and for sulfuric acid between 10 and 20% aqueous solutions. No particular advantage is obtained by going higher or lower than these values. Lower values than these would result in losses from lower conductivity, whereas higher values than these would tend to bring dragout losses higher than desired.

The bath temperatures should not be allowed to exceed 65 C. for oxalic acid and 30 C. for sulfuric acid in order to avoid dissolution of the coating. Generally, good coatings can be formed at temperatures as low as 25 C. and C. for the oxalic and sulfuric acid solutions,

respectively.

After anodizing the conductor may be further modified, if desired, by anodic treatment in an organic phosphate ester, stearic acid or sodium stearate to render the surface even more corrosion resistant and immune to futher hydration. As a consequence the rate of atmospheric corrosion is further reduced and the adhesion of ice, soils and other contaminants becomes lower.

Ohter methods which may be conveniently employed for preparing the improved conductor of the present invention includes conversion coating by immersion of the conductor in any of several different commercial formulations containing chromates or phosphates. These are introduced primarily to provide thin, oxide-containing surface films which improve the paintability or corrosion resistance; but in accordance with the present invention it has been found that these also improve the heat radiation capacity of a conductor by forming a thin, oxide-containing surface film thereby increasing the emissivity.

An additional method is the coating of the conductor with a slurry of aluminum oxide (boehmite). The conductor is subsequently heated to drive olf the water, thereby providing a hard adherent aluminum oxide surface.

The present invention will be more readily understood from a consideration of the following illustrative examples.

Example I Various aluminum conductors, all EC grade and identified in the table below, were immersed in an aqueous bath containing 7% oxalic acid and maintained at a temperature of 65 C. The conductor was maintained anodic with respect to a lead cathode and maintained at voltage for various times, as shown in the table below. After removal the conductor was rinsed with water and allowed to air dry. The emittance of the wire was then measured with results given in the following table. This table shows that conductor treated in accordance with this example has an increased emittance. In addition, all treated conductors had generally comparable physical properties and corroappearance, being light straw-yellow in color.

TABLE I Anodizing Measured Emittance Conductor 1 diameter All Aluminum None D 20 secs. a.s.i

40 sees. 20 secs.

Example 11 Lengths of EC grade aluminum conductor were immersed in a dilute aqueous sulfuric acid solution containing g./l. and maintained at 20 C. The conductor was maintained at 16 volts anodic during the anodizing period. The samples were then rinsed and air dried and the emittance measured. In addition, the thickness of the oxide coating was determined and is shown in the table below. This example shows that emittance is increased in accord.- ance with the anodizing treatment of the present invention. In addition, all treated conductors had generally comparable physical properties and corrosion resistance as the untreated and were less shiny in appearance.

TABLE II Oxide Emittance Thickness (mil) Anodizing Time (min.):

Example III TABLE III Treated Conductor Current (Amps) New Conductor Current (Amps) Temperature, 0.:

The higher current required to hold the temperature in the case of the treated conductor is due to the increased rate of radiation from the high emittance surface.

Example IV The commercial application of the foregoing treatments designed to increase emittance was applied to 1000 foot lengths of aluminum EC conductor, 7 wire, 0.5 diameter,

.on a continuous basis. Conductor entering the treatment was first passed through a stainless steel pipe 50 long containing a perforated inner tube, the purpose of the inner tube being to prevent contact between conductor and stainless steel. The stainless steel was anode cathode and the conductor anode. The electrolyte, 7% oxalic acid at about 54 C., was pumped through the stainless pipe and thence through a heat exchanger to remove sufficient heat to keep the electrolyte at constant temperature at the input end of the stainless pipe. End caps on the stainless pipes through which the conductor slides, prevents escape of the electrolyte. The conductor was passed through the pipe at a speed .of 20 feet per minute and the current was 500 amps per square foot.

Following this section, another similar one was used through which water is pumped to perform the rinsing operation. Air nozzles were placed before the rinse to remove excess oxalic acid. Similar nozzles in conjunction with heat guns perform the drying operation subsequent to the rinsing.

The conductor was finally fed to a take-up reel where it was coiled.

The resultant conductor was a pleasing yellow color with a surface oxide 0.15 mil thick and an emittance of about 0.8.

Example V The procedure of Example IV was repeated except that an additional final section was added similar to the anodizing section wherein the conductor is again treated anodically. In this case the electrolyte was a dilute aqueous solution containing 0.5% of a material containing about 65% by Weight of an ethoxylated octyl phenol phosphate ester, about 12% water and about 23% ethoxylated octyl phenol, see copending application S.N. 470,248.

The resultant conductor has the same properties as in Example IV, but in addition the surface has been rendered hydrophobic and largely immune to further hydration.

Example VI An all aluminum EC conductor was immersed in a conventional conversion coating solution containing 8 grams per liter of solution of hexavalent chromium and fluoride. The solution was maintained at 35 C. for 10 minutes followed by rinsing and air drying. The emittance measured after this treatment ranged from 0.42 to 0:50.

Example VII Samples of all aluminum EC conductor were sprayed with a solution consisting of boehmite in a colloidal suspension in water after which it was dried and heated to 100 C. for 15 minutes to form an adherent coating of boehmite of 0.28 mil thickness. Infrared absorption measurements of 0.2 mil aluminum oxide (boehmite) coatings show they possess equal or slightly better absorbance and therefore equal emittance to 0.2 mil anodic coatings prepared as in Examples I and II.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit .or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. An aluminum base alloy conductor of improved current carrying capacity having a diameter of at least 0.050" and having an IACS conductivity of at least 50, said conductor having a surface oxide coating of at least 0.01 mil thickness, the surface of said conductor having an emittance ratio of from 0.35 to 1.0.

2. An improved conductor according to claim 1 having at least three of said aluminum base alloy conductors stranded together to form a cable.

3. An improved conductor according to claim 2 having a steel reinforcing center cable.

4. A conductor according to claim 1 having a surface oxide coating of a thickness between 0.05 and 0.3 mil.

5. A conductor according to claim 1 having an emittance ratio between 0.4 and 0.8.

6. A conductor according to claim 1 wherein said surface oxide coating is an anodized oxide coating.

7. A conductor according to claim 1 wherein said oxide coating is a boehmite coating.

8. A conductor according to claim 1 wherein said oxide coating is conversion coated.

9. A conductor according to claim 1 wherein the surface thereof is hydrophobic.

10. A conductor according to claim 1 wherein said aluminum base alloy is EC aluminum.

References Cited UNITED STATES PATENTS 3,063,832 11/1962 Snyder 75-438 3,241,953 3/1966 Pryor et al. 29-l93 3,278,300 10/1966 Koike 75-l38 3,312,535 4/1967 Anderson et al 29183.5

HYLAND BIZOT, Primary Examiner.

RICHARD O. DEAN, Examiner. 

1. AN ALUMINUM BASE ALLOY CONDUCTOR OF IMPROVED CURRENT CARRYING CAPACITY HAVING A DIAMETER OF AT LEAST 0.050" AND HAVING AN IACS CONDUCTIVITY OF AT LEAST 50, SAID CONDUCTOR HAVING A SURFACE OXIDE COATING OF AT LEAST 0.01 MIL THICKNESS, THE SURFACE OF SAID CONDUCTOR HAVING AN EMITTANCE RATIO OF FROM 0.35 TO 1.0. 